1. Field of the Invention
The present invention relates to an image writing device, employed in an image formation device which prints the image written in a liquid crystal cell, for writing an image in the liquid crystal cell.
2. Description of the Prior Art
The U.S. Pat. No. 3,796,999 discloses a display in which laser beam is selectively directed to a liquid crystal cell to display an image on the liquid crystal. The theory of the display is that the heat of the laser beam is utilized to partially change the liquid crystal in phase and an image is formed corresponding to a pattern with which the laser beam is directed. The liquid crystal employed herein is, for example, a smectic liquid crystal.
Japanese Unexamined Patent Publication No. 20773/1989 discloses a device forming an image with the above-mentioned thermal writing type liquid crystal cell. Transmitted or reflected light of the liquid crystal cell is directed to photosensitive material to form a latent image on the photosensitive material, and an image is formed based upon the latent image. Further, a full color image can be also formed by using three liquid crystal cells having primary color R(red), G(green) and B(blue) images written to compose the three images.
With a prior art image formation device, when an image is written in a liquid crystal cell, an image of a single color is written in a single liquid crystal cell indifferent of the image density. As a result, when an image is of high density, the image is formed throughout the liquid crystal cell, but when the image is of low density, the image can be formed in only a part of the liquid crystal cell if it is desired that the image is written with the same density as a high density image. With a conventional method of writing an image, in order to form a composite image, image data of different colors must be written in different liquid crystal cells although the image itself is small. This is time-consuming labor, and there arises the problem that excessively long writing time is required.